1. Field of the Invention:
The present invention relates a method and device for controlling strain, deflection, and therefore stress, in a superstructure on maritime and aerospace vessels. Specifically, the present invention relates to naval vessels with superstructures that are prone to cracking due to design, material and/or installation flaws.
2. Description of the Prior Art:
With the advent of aluminum superstructures on board naval vessels, the use of expansion joints in the superstructure became common. These expansion joints were designed to isolate different sections of the superstructure and therefore prevent load transfer or buildup of strain in these sections. In general only the primary hull structure was used to resist the bending stresses caused by hogging and sagging conditions. Because of the material and the complexity of the expansion joints, maintenance problems became major concerns. Also, because there was no load transfer between isolated sections of the superstructure, there was no way to regulate the relative displacements between the sections. This condition created problems in operation of alignment critical equipment such as fire control directors, guns and launchers. Because of these problems, recent designs in naval shipbuilding have sought to eliminate the use of expansion joints. However, because of the complex stress distribution, and inherent flaws in the welding of aluminum, design level stresses have caused major cracking failures in the FFG-7, DD-963, DDG-2 and CG-47 Class ships. Therefore more recently, designs in naval shipbuilding have changed the superstructure material to steel in lieu of aluminum. While this solution reduces the cracking problem, a weight and stability problem becomes more prevalent. Steel superstructures weigh approximately 2 to 3 times more than those constructed of aluminum. In general, steel superstructures do not solve the cracking problem by controlling stress distribution, but rather by overdesign in terms of selection of material.